@KTtom could we make this a pinned topic for the summer months please?

This absolutely makes my blood boil

For anyone wondering about the issue of breaking a window to help the dog yourself:

S.5(2)(b) of the Criminal Damage Act 1971. In simple terms, you can commit damage to protect someone else’s property (a dog in this instance) so long as the property is in immediate need of protection and the means used are reasonable (a lawful excuse). In this kind of heat, a dog would clearly be in distress and I would gather evidence by video and photographs very quickly and make fast efforts to trace the owner, such as phoning the police who can use their systems to assist. If it’s outside a shop, try said shop for owner but spending ages going into different shops would be wasting precious time. All else fails, promptly smash a window.
Regarding the damage being reasonable to what you are trying to achieve, smashing a side window would be reasonable. Smashing several windows or smashing the windscreen would raise some questions as to why you thought that was necessary. You’d struggle to justify that if you are trying to get a dog out of a car.
If said dog was too large to fit through a side window, then that’s a different ball game and makes other options seem more reasonable.